The field of this invention is that of accelerometers, and the invention relates more particularly to silicon accelerometers incorporating piezoresistive sensing means.
Certain known silicon accelerometers comprise a silicon semiconductor member mounted on a base, the member having a mass mounted on a support by integral beams extending between the support and mass to permit movement of the mass relative to the base in response to an acceleration force. Portions of the semiconductor beam materials are doped to form piezoresistive sensors within the beams for sensing strain in the beams during movement of the mass to provide an output signal from the device corresponding to the acceleration. The sensors are interconnected in a bridge circuit to provide reduction in device sensitivity to off-axis accelerations. In such known accelerometers, the beams are arranged to permit selected movement of the mass in response to selected acceleration to provide the accelerometer with desired sensitivity to selected levels of acceleration force while also withstanding injury to the beams during application of the acceleration forces to the beams. It is desirable that there be substantial strain in the beams to be sensed by the piezoresistive means so that the sensor means provide an output signal of desired magnitude in response to the selected acceleration force levels. It would be desirable to improve sensitivity of the accelerometers while maintaining the desire ruggedness to withstand the acceleration forces.
In that regard, it is now recognized that the strains established in the beams in known accelerometers vary along the lengths of the beams and that the piezoresistive sensors have selected lengths extending along sections of the beams so that the sensors typically respond to the average strain in the beam sections occupied by the sensors rather than to the maximum strain levels in the beams. There also tends to be some variation in location of the sensors relative to portions of the beams having different strain levels therein during accelerometer manufacture so that the sensors may not be exposed to the highest or lowest strains in each of the beams in a uniform manner, thereby resulting in loss of uniformity of device performance and sensitivity from device to device during manufacture. Further, it is sometimes difficult to interconnect the sensors with convenient interconnection patterns to achieve desired reduction of device sensitivity to off-axis acceleration forces.